Psychodynamic explanations of demoniacal possession have been based mainly on Freud's retrospective interpretation of the illness of Christoph Haitzman. Freud applied libido theory to his analysis of the case and this subsequently influenced the psychoanalytic theory of paranoid symptom formation and the psychoanalytic approach to the psychoses. Fairbairn, and later Guntrip, applied an object relations theory to the case and conceptualized demoniacal possession in terms of bad internalized objects. They used the example of Haitzman to illustrate an object relations approach to the understanding and treatment of severely disturbed patients. In this paper the psychoanalytic treatment of a case of demoniacal possession is described to indicate the multiple dynamic meanings which possession may have and to demonstrate the necessity for integrating and applying aspects of libido and object relations theories. Current trends in psychoanalysis are towards recognizing the psychotic core which is frequently masked by an apparently psychoneurotic illness so that analysis must reach beyond oedipal conflicts to the primitive internalized object relations. A psychoanalytic study of demoniacal possession contributes much to the understanding of such patients but particularly to the conceptualization of borderline and psychotic states. It is in the treatment of these patients that the role of the psychotherapist is more akin to that of the exorcist.